Comparison of Compensatory Pituitary and Testicular Responses to Hemicastration Between Prepubertal and Mature Rats

Abstract

ABSTRACT: Prepubertal (14 days old) and mature (10 to 12 months old) male rats were hemicastrated and killed at selected intervals during a 12‐week period to compare the effect of age on acute and chronic pituitary and testicular responses to hemicastration. Testis weight was increased (P < 0.05) in hemicastrated (HC) prepubertal rats but not in mature rats compared with intact controls. After surgery, serum follicle‐stimulating hormone (FSH) concentrations were elevated (P < 0.05) by hour 12 and day 2 in prepubertal and mature rats, respectively, and remained elevated over control levels for 4 and 8 weeks, respectively. However, the magnitude of the rise in serum FSH following hemicastration was greater in the prepubertal animals. Pituitary FSH concentrations were increased (P < 0.05) by day 1 in prepubertal HC rats and remained elevated through week 4. In contrast, pituitary FSH levels were unaffected (P > 0.05) by hemicastration in mature rats. Serum concentrations of inhibin‐α were inversely related to serum FSH concentrations in prepubertal HC rats only. Serum testosterone concentrations were reduced (P < 0.05) following hemicastration in both age groups but recovered to control levels within 24 hours. Neither serum nor pituitary concentrations of luteinizing hormone (LH) were altered by hemicastration (P > 0.05) in either age group. In addition, there were no changes (P > 0.05) in the concentrations of testicular LH or FSH receptors following hemicastration throughout the 12‐week period. However, both receptor contents were increased (P < 0.05) in prepubertal HC rats in association with the increase in testis size. In summary, there were a number of age‐related differences in pituitary and testicular responses to hemicastration in the rat. Also, the rapid recovery of testosterone secretion in HC animals was apparently not associated with altered LH secretion or concentrations of testicular gonadotropin receptors.